In recent years, the occurrence of toxic organic compounds called endocrine-disrupting compounds (EDC) in wastewater and their fate during wastewater treatment plant has become an important environmental and health issues. EDC are exogenous substances or mixtures that alter the normal function of endocrine system and, consequently, cause adverse effects on population of living organisms or on their progeny. Effluents from sewage treatment plants can be discharged into rivers in the surrounding treated areas with EDC. Globally, a very low proportion of EDC participates to the total dissolved organic carbon (DOC<1%) of a contaminated water, but their presence in water has to be taken into account owing to their potential toxicity for humans (brain cancer, affection of immune and reproductive systems, e.g.) and aquatic species (feminization, toxicity to fish and invertebrates, e.g. Most of these organic compounds are stable and difficult to oxidize by the traditional biological methods and require further treatment. Modern legislation in every country imposes environmental regulation and heath quality standard that steadily become more restrictive. Different strategies need to be adopted by the wastewater treatment plants to comply with the variety of refractory organic pollutants. These compounds include alkylphenols such as bisphenol-A (BPA) used in chemical industries to make polymers such as epoxy resin, polycarbonate plastics and dental sealants, as a precursor of flame-retardants or as coreactant in thermal papers, and in its original form is discharged from chemical reaction processes and after thermal depolymerization. BPA were detected in the effluent at levels from 0.16 to 0.36 μg/L. According to prior studies, in municipal wastewater and sewage sludge, BPA concentrations were found within the range of 0.033-36.7 mg/g in Canada, within 30-330 mg/g in Germany, and at 28.3 mg/g in China, indicating that BPA is not completely eliminated during wastewater treatment, and the maximum concentration of BPA detected was 17.2 mg/L in waste landfill leachates. Thus, wastewater treatment plants (WWTPs) are significant point sources of surface water pollution. Even though endocrine low dose effects of BPA are still under discussion it was recently demonstrated that low concentrations of BPA (even below 1.0 μg/L) in aquatic ecosystems had adverse effects (Oehlmann et al. Ecotoxicol. 9 (2000) 383-397).
Membrane treatments can be used as alternative methods to efficiently remove refractory pollutants from wastewaters. Removal of inorganic pollutants such as nitrogen (NH4—N) was reported in literature using membrane bioreactors (MBR) where 93% removal of NH4—N from synthetic wastewater was recorded, using MBR operating at solid retention time (SRT) of 7 d, HRT of 5 h, and TSS of 10 g/L, and 95% removal of NH4—N from municipal synthetic wastewater was observed using MBR equipped with hollow fibre ultrafiltration membrane. A weak rate of biological removal of phosphorus in MBR, ranging from 45 to 70% was observed. However, the submerged membrane activated sludge process enables treated raw water with a high biomass concentration and long residence time. This coupling of membrane with activated sludge offers the possibility for high pollutant removal and low sludge production.
Other previous studies have reported that adsorption onto sludge, biodegradation and transformation are major pathways for BPA removal in activated sludge process. These mechanisms occurred in MBR however they may be different because of the different characteristics and properties of the MBR sludge. High SRT and biomass concentrations in MBR involve reevaluating adsorption and biodegradation mechanisms in order to integrate: i) easy access of pollutant to active adsorption sites of sludge due to the decrease of transfer limitation, induced by the less flocculated microorganisms, ii) intensified hydrolyze of macromolecules (retained by the membrane) which increases their retention time to become equal to that of particular mater, and iii) specific biomass composition.
Therefore, there is a need for processes for reducing bisphenol compound content of a wastewater using a membrane bioreactor.
Furthermore, there is a need for monitoring and regulating processes for reducing bisphenol compound content of a wastewater in a membrane bioreactor.